I'm local, so I can give you more information than those that have only raced. First and foremost, checkout
https://rootsrated.com/ironman-chattanooga. It has lots of great information. Second, I think people are nuts to drive from Atlanta or Nashville to only save a few dollars on flights. Both Nashville and Atlanta can get very congested plus you will need to arrive 2 hours or more early for your flight. In Chattanooga you can get there 30 minutes before the flight and be fine. It's not worth the hassle for a few dollars. Third, almost every hotel in downtown Chattanooga will be fine. I would recommend any hotel north of MLK Boulevard. Fourth, the temperature and humidity can be high. I believe the race is the second weekend in September. That is usually when the summer heat starts to break. This year was hot. For instance, September 10th was 95F for a high with the humidity at 81 percent. Other years it has been lower. Finally, the course will be different the IM Chattanooga or IM Chattanooga 70.3. I've been told it will be going over Lookout Mountain which I think is awesome! But who knows (other than Brian).
Congratulations and enjoy our awesome city!
P.S. Make sure to follow Brian. He knows what he is talking about. :)